Common types of photovoltaic deployment include off-grid and on-grid systems. Off-grid systems are typically small (e.g., 10 s of kilowatts at most) and tied closely to an energy storage system such as a system of deep-cycle lead acid batteries or, in some cases, to a fueled gen-set. In an off-grid configuration, the energy stored in the battery acts as a buffer between energy production and demand. As such, short-term variability, such as peak collection, in the solar resource may not be an issue. On-grid systems, by contrast, may be quite large, with systems up to the 100 s of megawatts. To date, sizing of on-grid systems may be such that existing methods of handling load variability (e.g., by provision of ancillary services from generators on the grid) have been sufficient to ensure stability of the grid.
However, with advances in photovoltaic system technology, ever larger systems are being proposed and actually installed for use. Such larger systems may pose challenges for power management in at least two end markets, e.g., in island- or micro-grid systems or in very large photovoltaic plants integrated onto large grids. In either case, there may be restrictions on the maximum solar energy collection capability with respect to the sizing capability of an associated power conditioner of a power plant. Typically, the proposed method of managing peak or variable output of renewable generating resources is to add an energy storage component or to subdue plant power production. However, there may be a lack of reliable, commercially proven, and cost effective storage unit compatible with a facility scale at the 100 s of kilowatts level or higher, or there may be issues associated with inverter controls or power conditioning controls at an inverter.
Furthermore, one of the major challenges for solar photovoltaic power plants may be that, at present, owners and operators have very little control of the electrical output of a power plant in the short-term (e.g., on the hours and minutes scale). Having more control over the output of the power plant may be desirable since such control may be used to ensure that plant operations are increasingly economic or practical. More control may also become a minimum requirement for some large photovoltaic power plants, due to limitations of the existing electrical grid and its ability to cope with load variability. The current lack of output control in the hourly or minutely timeframe may be due to at least two independent factors: (1) the inherent short-term variability of sunlight due to cloud cover and other weather phenomena, and (2) the technological state of the art for a photovoltaic power plant may be such that the instantaneous electricity output of the plant directly correlates to the amount of sunlight received at each moment.